The purpose of these studies is 1) to determine the validity (sensitivity, specificity) and reliability of the enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of toxocaral visceral larva migrans (VLM), and 2) to measure the prevalence of antibody in several populations of children (cross-sectional analysis), and to determine the epidemiologic characteristics of persons with normal and positive titers (case-control approach). These studies should enable us to assess the public health implications of environmental contamination with this nematode, to identify and quantitate the risk factors associated with infection, and to formulate recommendations for primary and secondary disease prevention.